Condit, Richard C: Professor Emeritus
Poxvirus genetics and molecular biology with an emphasis on 1) regulation of transcription elongation and 2) virus assembly.
Vaccinia is a large double stranded DNA-containing poxvirus that replicates in the cytoplasm of infected cells. The cytoplasmic site of replication requires that the virus encode virtually all of the functions required for both mRNA and DNA metabolism. Thus over the years vaccinia has served as a very useful model system for understanding mRNA synthesis and modification. In addition, the virus must assemble a complex membraned particle in the cytoplasm, in part by co-opting cellular machinery and in part using unique virus coded functions. Our laboratory has sought to elucidate novel elements in control of transcription and virus morphogenesis through the isolation and characterization of conditionally lethal mutants of vaccinia virus.
In recent years it has become increasingly clear that transcription elongation is an important control point for regulation of eucaryotic gene expression. Our recent work demonstrates that postreplicative gene transcription elongation is regulated during vaccinia virus infection. A study of this regulation is important for understanding regulation of vaccinia virus gene expression in particular, and the system may prove to be an important model for study of regulation of transcription elongation in eucaryotes in general.
Transcription elongation is an important control point for regulation of eukaryotic gene expression. Our work demonstrates that postreplicative gene transcription elongation is regulated during vaccinia virus infection. A study of this regulation is important for understanding regulation of vaccinia virus gene expression in particular, and the system may prove to be an important model for study of regulation of transcription elongation in eukaryotes in general.
The specific goal of this project is to understand the regulation of vaccinia virus postreplicative (intermediate and late) gene transcription elongation. The effort currently centers on four vaccinia genes, A18R, G2R, J3R and H5R, which seem to regulate postreplicative gene transcription elongation with complementing activities. Genetic and biochemical experiments suggest that A18R is a transcription termination factor and that G2R, J3R and H5R are positive transcription elongation factors. Our working hypothesis is that these gene products work together, perhaps as a transcription elongation complex, to regulate formation of 3′ ends of intermediate and late vaccinia viral mRNAs. Efforts are underway to test, refine, and extend this hypothesis through (1) an in vitro transcription elongation assay, (2) phenotypic analysis of existing virus mutants defective in transcription elongation, and (3) isolation and characterization of additional elongation defective mutants.
The vaccinia virion is a complex membraned particle containing nearly 80 viral proteins, including both structural proteins and a large cache of transcription enzymes. The virion is assembled in the cytoplasm in virus factories using a combination of cellular and virus specific pathways. Numerous virus mutants have been identified which affect the assembly process, and characterization of these mutants provides insight into the specific role if individual virus proteins in virion assembly. Our recent and current work focuses on three virion core proteins, the products of genes A3, E8 and E6, which affect virion core assembly. Our long term goal is to understand the substructure of the virion core as it relates to virion assembly and function.
Awards, Professional Service:
Editorial Board, Journal of Virology
Associate Editor, Virology
Member, NIH virology study section (1990-1993)
Chair, DNA Viruses Division, American Society for Microbiology (2002)
Chair, Program Committee, American Society for Virology, (2004-2005)